On 10/26/2016 08:27 AM, stepharo wrote:

So what is the definition of printShowingMaxDecimalDigit:?
I have the impression that there is a confusion between the rounding a number and the printing of his value in a given format.

Yes, I see quite a bit of confusion in this thread about that.

we can deprecate roundTo: if necessary.

I think roundTo: is OK. #round: is not, and should be deprecated (at least for Floats). For Floats, the idea of rounding to a specific number of decimal digits is a fantasy. Here's why: Floats cannot exactly represent most common decimal fractions. For example:

0.1 -- not representable

0.2 -- not representable

0.3 -- not representable

0.4 -- not representable

0.5 -- hey, representable!

0.6 -- not representable

0.7 -- not representable

0.8 -- not representable

0.9 -- not representable

1.0 -- representable.

*Printing* a Float to a specific rounded decimal format is a sensible idea, and should be encouraged. But trying for a "rounded Float" *number* just can't be done exactly (except by converting to a Fraction).

Fractions can be rounded to exact decimal fractions, so something like "myFraction roundTo: 1/100" makes sense. But the current implementation of round: on Fraction that converts to a Float just gets you the misery detailed above.

On 10/26/2016 01:00 PM, Nicolas Cellier wrote:

I've put a single slice in the inbox for the 3 issues because they all are related.

See slice comment:

For Float, implement guard to prevent overflow (15471), and use exact representation for intermediate results (asFraction) so as to avoid double rounding problems (15473)

The double rounding problem is not the fundamental problem, the fundamental problem is that what is desired does not exist, because Floats cannot exactly represent most decimal fractions. So this can't really fix it.

For Fraction (15472), choose an exact representation for result rather than Float. This is because such method is particularly usefull for financial/monetary applications.

Yes. Fraction or ScaledDecimal. Not Floats, unless the developer understands the needs of the financial world and the limitations of Floats very well.

Regards,

-Martin